Recently, various patterns are formed on various magnetic recording media for practical and design purposes.
It is particularly important for magnetic cards requiring sophisticated designs such as credit cards and bank cards to have a high quality design. Conventionally, colored magnetic stripes are known, which are formed by providing a colored layer on the magnetic stripe on a card base material to completely conceal the black or brown color of magnetic recording layer which is inherent in magnetic powder. Recently, pattern formed magnetic stripes are also produced, which are formed by providing a pattern on the magnetic recording layer or on the colored layer on the magnetic recording layer.
In order to form such a pattern formed magnetic stripe, as shown in Procedure of FIG. 11, a release layer and a protective layer or a releasable protective layer is formed on a temporal carrier base; a pattern is formed thereon; a colored layer to conceal the hue of the magnetic recording layer, a magnetic recording layer, and a heat-sensitive adhesive layer are further formed in sequence so as to form a laminate; and the laminate is cut to a desired width to produce a transferable laminate for forming a magnetic stripe.
The transferable material of the magnetic stripe-forming transferable laminate obtained as described above is transferred on the overlay sheet of a card base and heat-pressed with the center core and the overlay sheet on the opposite side to obtain a pattern formed magnetic stripe card having the magnetic stripe transferable material embedded in the overlay sheet (see FIG. 1).
However, the pattern formed magnetic stripe formed as described above has a pattern on the magnetic recording-reading side of the magnetic recording layer. Therefore, the spacing, or the distance between the magnetic head and the magnetic recording layer during the recording/reading, varies between the patterned area and the non-patterned area and, accordingly, reading output-fluctuations occur. Consequently, the chance of possible information reading errors tends to be increased.
A disclosed method to eliminate the level-difference between the patterned area and the non-patterned area due to the pattern-formation is to fill the space of the non-patterned area using the negative pattern of the patterned area (see Patent Document 1). The negative pattern printed in the non-patterned area can be more indistinctive for further effects of the filler ink when the colored layer (concealing layer) formed on the entire patterned area and the space-filler ink applied to the recess of the non-patterned area have the same hue. This method has a certain effect on reducing the output fluctuations due to the level-difference, but it is not perfect. Furthermore, an additional coating step of filling the non-patterned area is required, which inevitably reduces the production efficiency.
In order to resolve the above problem, a method of producing a magnetic tape is proposed in which a concealing layer and a resin coating layer that can be dyed using a disperse dye are formed on a magnetic recording layer and the resin coating layer is dyed using a sublime disperse dye (see Patent Document 2). In this method, the level-difference due to the pattern-formation is prevented; however, the formation of the resin coating layer is necessary for settling the dye in addition to the concealing layer. Also, it is generally difficult to obtain both excellent sublimation and stability in sublime dyes. Therefore, the formed pattern does not always have sufficient weather-resistant storage stability and stability over time. Furthermore, in this method, a pattern is formed on the outermost resin coating layer using a sublime dye and a protective layer is then formed thereon. That is, the laminate is not formed at a time in the transfer process. The process is divided and, therefore, the production efficiency is reduced.
On the other hand, it is known that some magnetic cards with which security is an important issue such as credit cards and bank cards carry a pattern formed on the magnetic recording layer using infrared ink or a fluorescent agent as a special pattern for anti-counterfeit measure. These patterns are usually invisible. Their position and presence is concealed and, importantly, they are recognizable only using a specific light source or detector. However, when the level-difference due to the pattern is observed, the security level is lowered as described below.
For example, a fluorescent pattern formed using a fluorescent agent should be invisible under ultraviolet light in the sunlight or room light as described above. It should be recognized as a fluorescent pattern only using ultraviolet light emitted from a special ultraviolet light irradiator to confirm the authenticity of the card.
Therefore, a concealing layer is formed on the area where the fluorescent pattern is formed and the fluorescent pattern is recognized only when irradiated with intensive ultraviolet light using a special ultraviolet light irradiator (see Patent Document 3).
However, the concealing layer usually has a thickness of several μm or smaller so as to reduce loss in reading output. Therefore, it is difficult to completely eliminate the level-difference of the fluorescent pattern. Even if the fluorescent pattern is unrecognizable in the sunlight or under the room light or the like because of the concealing layer, the remaining level-difference formed by the fluorescent pattern and never completely eliminated inconveniently makes the pattern visible because of the reflection of light. Such a remaining level-difference causes reading output-fluctuations and deteriorates signals in quality.
In order to resolve the above problem, a method of producing a magnetic card having a fluorescent pattern is disclosed in which a release layer, an overcoat layer, a pattern printing layer, a concealing layer, and a fluorescent pattern-forming area are laminated on a temporal carrier base in sequence to form a transferable material and the transferable material is transferred to a card base material where a magnetic recording layer is previously formed in the transfer step (see Patent Document 4). In this method, the ink in the fluorescent pattern-forming area formed on the concealing layer is appropriately impregnated into the concealing layer so that the fluorescent agent impregnated in the transferred concealing layer produces fluorescence under ultraviolet light. The fluorescence is not blocked by the concealing layer or no level difference due to the fluorescent pattern occurs. However, the ink composition and the resin composition of the concealing layer have to be carefully selected to properly impregnate the fluorescent agent into the concealing layer. The fluorescent pattern may highly possibly be blurred or fail to provide sufficient emission intensity as a result of slight changes in procedure. Therefore, a limited selection of inks and resins and a limited degree of freedom in design are imposed.
Furthermore, in the prior art method of producing a pattern formed magnetic recording medium in which a pattern is formed on the magnetic-stripe part through the transfer step has the following inconvenience. The pattern is printed on the transferable laminate usually after a release layer and a protective layer or a releasable protective layer are formed on a temporal carrier base. Then, a colored layer, a magnetic recording layer, and a heat-sensitive adhesive layer are laminated in sequence. In other words, the pattern has to be printed in the earlier stage of the production of a magnetic stripe-forming transferable laminate. After a pattern is determined and produced, many more steps and time is required to produce a magnetic stripe-forming transferable laminate. Therefore, when the pattern has to be modified after the patterned magnetic stripe-forming transferable laminate is completed, the pattern cannot be modified in a short time and the pattern-modification is a major cause of significantly delayed delivery and reduced performance.
When the pattern is formed on the magnetic recording layer of a magnetic recording medium as described above, the pattern often undergoes deteriorated signal properties or fails to fulfill the expected function as the sophisticated design or anti-counterfeit.
Furthermore, the prior art method of producing a pattern formed magnetic recording medium does not offer excellent production efficiency.    Patent Document 1: Japanese Unexamined Patent Application, Publication No. S59-168933    Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2000-155937    Patent Document 3: Japanese Unexamined Patent Application, Publication No. 2000-002160    Patent Document 4: Japanese Unexamined Patent Application, Publication No. H09-309287